The Advanced Television Systems Committee (ATSC) has developed a standard for broadcast of digital television in the United States over defined TV frequency bands. Among other countries, the ATSC standard has been adopted in Canada, Mexico, and is under consideration in even more countries. The evolution of TV broadcasting from analog to digital, however, has led to the opening of some TV channels in the TV frequency bands known as “TV white spaces” (TVWS) to unlicensed operation of secondary devices, also known as white space devices (WSD), that operate within what is known as cognitive radio (CR) systems provided that such devices avoid interference with licensed (incumbent) services such as digital TV and wireless microphones.
Devices or equipment operating in the TV frequency bands must follow Federal Communications Commission's (FCC) regulations, which requires that the quality of the primary service should not be degraded by the operation of the WSDs.
The terms “secondary devices” or “cognitive radios” are used herein interchangeably to designate devices operated by un-licensed users. Similarly, the terms “primary services” and “incumbent services” is used herein interchangeably to designate services operated by licensed users, while “primary devices or “incumbent devices” are used to designate devices that operated with “primary services” and “incumbent services.” The term “free channel” or “white space channel” is used here to designate a TV channel that is not currently in use by a primary service or incumbent device. The term “wireless devices” or “devices” is used to designate a variety of devices including, and not limited to mobile telephones, portable computers, stationary computers, portable handsets, etc.
The FCC rules further require that manufacturers of WSDs or secondary devices to contact an authorized database system to obtain a list of channels that are authorized for operation (i.e., channels not protected for incumbent services). So far, FCC has authorized a number of TV White Space Database Administrators (TVWSDA) to provide TVWS database service to WSDs. One such TVWSDA is Telcordia Technologies, which is a member of the TV White Space Database Group that implemented a specification for database-to-database (DB-DB) interface with TV white space (TVWS) databases authorized by the FCC.
Channel use authorizations are determined for a specific location. In an authorized system, the operating white space devices are required to provide their geographic location by means of a secure Internet connection to a TVWS database. The TVWS database will return a list of authorized channels available for operation by the WSDs for their reported locations. A web portal is used to register protected primary devices and services entitled to protection as authorized by the FCC rules. These devices and services include: low power auxiliary stations, including wireless microphones, Multi-Channel Video Programming Distributor (MVPD) receive sites and Broadcast Auxiliary links (cable headend receive sites).
A TVWS database includes data associated with registered “protected entities” including user IDs, Owner/Registrant and Contact information. MVPD receive sites, wireless microphone users, and operators of temporary BAS links must specifically register their sites with an authorized TVWSDA to receive protection from white space devices. The database services provides a registration site to register for protection from white space device interference on a channel or channels as permitted by the FCC rules at a geographic location.
Some TVWSDAs offer channel availability calculator/contour visualization tools to see the channels available for white space devices at a geographic location or to view protected contours on a map or view the details of protected entities. The TVWSDAs compute “protected contours” for licensed services including TV and wireless microphone services using propagation models. They also record other “keep out” areas such as border regions of U.S. with Canada and Mexico. These protected contours and keep out areas are based on FCC regulations which aim to protect licensed services. A TVWS database allows a WSD to use a channel if the WSD is outside these protected contours and keep out areas.
Therefore, WSDs need to be equipped with spectrum usage and management capabilities in order to meet the FCCs requirements. As such, WSDs are required to identify free, or unused, channels in the TV bands, and/or identify channels that are occupied by incumbent services. If a incumbent service is identified, the secondary user is required to seek other channel(s) or delay its use of the channel(s) until the incumbent ceases to use the channel(s).
In a CR system within which WSDs operate, frequency resource allocation determines channels or frequency bands for the CR system to use. The frequency resources are provided by a frequency resource provider, for example a TVWSDA, in a specific locality. The frequency resource is allocated by a frequency band allocator, and is then used by resource users. An existing frequency resource allocation scheme includes a TVWS database, which provides a list of TV channels available for the CR system to use. A resource allocator decides which channel(s) to use, and notifies the resource user. The resource user uses the channel(s) to operate.
This approach has a number of drawbacks. One drawback is that the propagation model used to compute protected contours may not be accurate, resulting in over-protection of incumbent services and prohibiting WSDs from operating at locations where such devices can operate without interfering incumbent services. These locations may include deeply shadowed areas inside protected contours and indoor areas where building attenuation protects outdoor incumbent services from interference from indoor CR operation. Another drawback is that the propagation model may not be able to catch non-stationary changes over time. These changes may result from weather and traffic. Moreover, some transmitters using the frequency resource may not be recorded in the database. For example, a TVWS database only has records on registered licensed services. All unregistered incumbents are not taken into consideration in the database.
These drawbacks prevent a database to provide reliable quality measures on frequency resources. Here, the quality of a frequency band is measured by the interference the CR system may generate to incumbent services and the interference level and types the CR system may suffer from other users.
Accordingly, there exists a need to prevent interference to incumbent services, while optimizing frequency resource utilization to improve CR system performance and achieve better coexistence among CR systems.